Research by Scott Bogner

First principle calculations of medium-mass nuclei

by Scott Bogner

The nuclear shell model has proven invaluable for interpreting data and making predictions to guide experiments. Together with Heiko Hergert (MSU) and external collaborators Jason Holt (TRIUMF) and Achim Schwenk (Darmstadt), we have applied the recently developed
In-Medium Similarity Renormalization Group (IM-SRG) method to understand how the shell model, where one models the nucleus as an assembly of weakly-interacting valence nucleons moving in an average potential well, emerges from the strong two- and three-nucleon forces that are known to exist in nature. The IM-SRG has previously been used with great success in first principle calculations of ground state energies of medium-mass closed-shell nuclei. Recently, we extended the method to construct effective valence shell model hamiltonians starting from realistic NN and NNN matrix elements from chiral effective field theory [1]. This opens up the exciting possibility for first principle spectroscopic calculations in open-shell medium-mass nuclei. Our preliminary successful description of spectra in the oxygen chain maintains a transparent connection to the underlying nuclear forces, while being competitive with calculations with phenomenological shell model interactions such as the USDb Hamiltonian developed by Alex Brown (MSU) and collaborators. A sampling of our results for ²²O and ²³O are shown in the Figure, where one sees a) the decisive role played by NNN forces to obtain good agreement with experiment and b) a substantial improvement over previous methods to construct shell model hamiltonians using many-body perturbation theory (MBPT).

[1] S.K. Bogner, H. Hergert, J.D. Holt, A. Schwenk, S. Binder, A. Calci,  J. Langhammer and R. Roth, Phys.Rev.Lett. 113 (2014) 142501.